This invention relates to a process for demetallation in oils/fats most preferably vegetable oils/animal oils/fats. The metal mainly includes P, Na, K, Ca, Mg, Cu, Fe etc. The present invention is an environment friendly, industrial effluent free novel process, which includes avoidance of any water washing process during counter-current treatment with recycled and fresh clay in one or more stages. The inventive process also avoids usage of any expensive industrial chemicals that are used in prior art. The process finally includes treatment of oils/fats with ion exchange resin to make the oils/fats suitable for feedstocks for catalytic refining processes, such as hydroprocessing/FCC. The present invention increases the shelf life of the oils/fats by reducing total metal contaminant below 1 ppm. Thereby the present invention provides a very cost effective process to produce total metal contaminant free oils/fats.
Conventionally, biodiesel is produced by transesterification of vegetable oil, which are triglycerides of C14 to C22 straight-chain unsaturated carboxylic acids. In the process, triglycerides are converted into Fatty Acid Methyl Esters (FAME) with an alcohol in the presence of a catalyst. The process though simple suffers from several disadvantages. The removal of glycerin needs separation, excess of methanol is necessary to complete the reaction and subsequently its recovery. There are steps of water washing to remove the caustic and this adds to the plant effluent. Moreover if the vegetable oil is rancid, an additional step of esterification is necessary. The process is suitable only for oils having low Free Fatty Acid (FFA) <0.5%.
Biodiesel has several inherent problems such as high density of about 0.88 g/cc (diesel density 0.825 to 0.845 g/cc) and narrow boiling range 340° C.+. Any further reduction in T-95 specification will affect refiner's profitability adversely due to requirement of production of lighter diesel for enabling blending of biodiesel. The presence of oxygen in biodiesel also results in higher emissions of NOx. Also, FAME is not well accepted by auto industry in all proportions as these are responsible for injector coking.
To overcome the above difficulties, Refiners are exploring hydroprocessing route, as an alternative option, and produce renewable fuels such as diesel, ATF, gasoline etc from vegetable oils/animal oils/fats. This will enable integrated refining and marketing companies to meet stipulation of blending biofuels in diesel that may be mandated by the Government in near future. The process results in improvement in quality of diesel particularly w.r.t. cetane number and density. The process is capable of handling different vegetable oils; however, it is required to pre-treat the oil to remove metals below 1 ppm to avoid faster catalyst deactivation.
Vegetable oils and animal oils/fats typically contain about 50-800 ppm of metals such as P, Na, K, Ca, Mg, Cu, Fe etc. In crude vegetable oil, these metals can originate from contamination by soil and fertilizers. The phosphorous is present as phosphorous based compounds (phosphatides). The presences of these compounds impart undesirable flavor, color, and shorten the shelf life of oil.
Metals such as Fe and Cu are usually resulted from corrosion and mechanical wear at the mills and refineries. These metals are prooxidant and thus, detrimental to the oil quality. Trace metals may be present as complexes surrounded by proteins, phospholipids and lipids or non-lipid carriers. These metals catalyze the compositions of hydroperoxides to free radicals. Fe increases the rate of peroxide formation while Cu accelerates the hydroperoxides destruction rate thereby increasing the production of secondary oxidation products.
Conventionally, water acid degumming is used to remove phosphatides from vegetable oils and animal oils/fats. This process is being used as part of biodiesel manufacturing plant. In this process oil is heated up to about 70-90° C. followed by mixing of 0.05 to 0.1% phosphoric acid in a Continuous Stirrer Tank Reactor (CSTR). The residual acid is neutralized in subsequent CSTR by mixing with caustic followed by removal of gums by centrifugation and water washing. The process requires huge quantity of water for water washing and its disposal. Caustic used for neutralization of residual phosphoric acid also reacts with free fatty acids present in oils and fats and forms stable emulsion which is very difficult to break and requires longer time. The process is not suitable for removal of trace metals below 20 ppm.
U.S. Pat. No. 5,239,096 disclosed a process for reducing non-hydratable gums and wax content in edible oils. The process involves mixing with 0.01 to 0.08% acid (in the form 10-15% aqueous solution), adding 1-5% base solution followed by slow mixing for 1-4 hrs, separating gums and water washing of oil. As discussed above the process will suffer due to drawbacks of water washing and neutralization steps.
U.S. Pat. No. 6,407,271 disclosed a method for eliminating metals from fatty acid substances and gum associated with said metals. Method comprises mixing of vegetable oil with aqueous solution of salt of polycarboxylic acid (Sodium salt of ethylenediaminetetraacetic acid, EDTA) in the droplets or micelles in the weight ratio above 3. The aqueous phase is separated from oil by centrifuging or ultra filtration. Process uses very expensive chemicals and huge quantity of water about 33% of vegetable oil.
U.S. Pat. No. 6,844,458 disclosed improved refining method for vegetable oils. In this method aqueous organic acid and oil subjected to high and low shear followed by centrifuge to remove gums. As cited in examples process uses about 10% water of oil quantity to dilute the acid solution and treated oil still contain about 20 ppm of metals.
U.S. Pat. No. 7,494,676 disclosed a pretreatment process comprising of a) enzymatic degumming with or without citric acid and sodium hydroxide b) bleaching with 2-4%) bleaching earth and 0-1% activated carbon c) dewaxing at low temperature of 18-20° C. with gentle stirring for about 12-18 hrs to achieve <5 ppm phosphorous. The process uses up to 2.5% of water and centrifuge for separation of gums. As described above, caustic react with free fatty acids present in oil and fats and forms stable emulsion which is very difficult to break and require longer time. The complete process takes very long time of about 15-20 hrs. Hence the size of dewaxing vessel will be huge and also require high energy for stirring. Moreover, process did not discuss the removal of other metals such as Fe, Cu, Na, K, Ca, Mg etc. present in the oil.
Hence, there is need of simple and suitable process which can avoid use of water and expensive chemicals and reduce total metal contaminant below 1 ppm to make the oil or fat suitable for catalytic processes such as hydro processing/fluid catalytic cracking.
There is also a need to provide a demetallation process suitable for removal of total metals below 1 ppm in vegetable oils such as jatropha carcass oil, karanj oil, castor oil, ricebran oil, soybean oil, sunflower oil, palm oil, rapeseed oil etc and animal oil/fats such as fish oil, lard etc. Further, avoidance of water washing makes the process environment friendly and effluent free. Likewise, centrifuging steps in the process need to be avoided.